Forage harvesters are machines which handle the cutting down of crops in the field and subsequent processing of the relevant crop into a state suitable for animal consumption. This may involve picking up crops, such as grass or alfalfa, which have been pre-cut and allowed to dry off in the sun, or it may require the forage harvester to cut crops, such as maize, directly from the fields.
The crop, whether cut maize or gathered grass, is fed into a rotating knife drum or cutter which chops the product to a suitable length. With grass crops, cutting alone is sufficient to produce the desired forage. When harvesting maize for silage purposes, the cutting alone does not yield enough grain due to the presence of kernels in the crop. The kernels need to be cracked in order to extract the grain as un-cracked kernels are difficult for animals to digest. As cutting alone is insufficient to crack all the kernels, it is supplemented by a further process which passes the cut crop through a kernel cracking assembly, also known as a crop processor. This consists of two close, adjacent rollers, typically having fluted or serrated surfaces, which rotate such that there is slippage between the adjacent surfaces. The gap between the rollers is tailored to the desired diameter of grain passing through and the speed, rotational energy of the rollers, relative movement and fluting of the surfaces ensures that any un-cracked kernels are cracked.
The kernel cracking assembly performs best when the distance between the rollers is small and constant. The performance of the crop processor decreases when the separation of the rollers increases because fewer kernels are cracked. For optimal performance this distance needs to be monitored and adjustable by the operator of the machine.
A crop processor known from U.S. Pat. No. 6,290,599 attempts to solve this problem by controlling the relative positions of the rollers by means of two adjustable stops in the form of plungers which are movably guided in hydraulic cylinders, each arranged at a respective axial end of rollers.
These are problematic in that the rollers are actively moved at both ends by different plungers which, despite being hydraulically coupled, are prone to leak at different rates, causing their displacement to differ slightly from one another. This in turn leads to the rollers being non-parallel and thus less efficient at cracking kernels.
There is therefore a need to carefully control the separation of the rollers and their alignment in order to maintain the efficiency of the kernel cracking assembly.